Protesters took to the streets in towns and cities across Tunisia for a fourth day Friday, as anger grows over price hikes introduced by the government. Demonstrations in 2011 in Tunisia grew into the revolution that overthrew the government and triggered a wave of uprisings across the Arab world. Seven years on, the dictatorship may have gone but, as Henry Ridgwell reports, lingering social and economic problems are driving the anger, raising the prospect that the unrest could spread.